164273

I discovered that when the numbers are added diagonally there is a pattern because the answer is repeated. (E.G 1 + 4= 5, 3 + 2= 5; 5 + 8 =13, 7 + 6 =13). The pattern of diagonally opposite sums will be 5, 5, 13, 13, 21, 21 29, 29, 37, 37, 45, 45, 53, 53).

I then noticed another pattern, which is that there will be a difference of 8 between each of those answers. But I can't work out why at this stage.